Does Chain Lightning deal damage to its original target first?

Question

When Chain Lightning deals damage, does it deal damage to all targets at once, or does it's original target takes damage first? I ask this question because after damage was taken concentration checks were made on spells, the primary target concentrating on bless who failed, and a secondary target concentrating on haste who passed with bless on but not if it was off. The DM ruled that the primary target takes damage first so there was no bless, so the second concentration failed which ended haste as well, wasting a turn on our martial.

Answer 1

Yes, because "then"

First off, your DM ruled that the primary target took damage first. Just that is enough - your DM is, by definition, correct in their own game.

Now, if your DM made it clear that this was their 'ruling at the time' but that they were open to considering other viewpoints, then consider showing them the answers this question receives.

'Then' implies an event that happens later

Chain lightning says (emphasis mine):

You create a bolt of lightning that arcs toward a target of your choice that you can see within range. Three bolts then leap from that target to as many as three other targets, each of which must be within 30 feet of the first target.

By saying the first target is struck by the lightning, then the lightning leaps to the other targets, the spell description is establishing that the damage to the secondary targets happens at a later point in time. Even if imperceptivity later, it is enough time for the first target to have failed their Concentration save and the secondary targets to have lost their bless before they are struck. However, there is no time difference between when each of the secondary targets are struck because the spell does not indicate any, even if one of them is sharing a square with the target and another is 30' away.

One spell, one damage source?

You might think ok, there is an infinitesimal time delay between when the first lightning strikes and the arcs to the secondary targets. But it is all one instantaneous spell - shouldn't all the damage resolve at the same time?

Let's consider the wording in two other spells: Ice Storm vs. Ice Knife, and note that both of them are, like chain lightning 'instantaneous'.

Ice storm says:

A creature takes 2d8 bludgeoning damage and 4d6 cold damage on a failed save,

Because this is simply 'bludgeoning damage and cold damage', it is just one instance of damage, and someone concentrating on Bless but hit with ice storm would need to make one Concentration save, only. If the spell had said '2d8 bludgeoning damage and then 4d6 cold damage', the two sources of damage would have been separated in time and two saves would have been required. For what that looks like, let's go to Ice Knife.

Ice Knife says:

On a hit, the target takes 1d10 piercing damage. Hit or miss, the shard then explodes. The target and each creature within 5 feet of it must succeed on a Dexterity saving throw or take 2d6 cold damage.

The fact that the piercing damage is dealt, and then the cold damage is taken means that this is two different instances of damage separated in time and two Concentration saves would be required.

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_{Other, similar, questions on this site have answers saying that all the damage happens at the same time because the spell's duration is instantaneous. This is a common mistaken assumption.}

_{'Instantaneous' as a spell duration does not mean that the spell itself takes no time. Instead, the definition of 'instantaneous' is:}

_{Many spells are instantaneous. The spell harms, heals, creates, or alters a creature or an object in a way that can't be dispelled, because its magic exists only for an instant.}

_{Features do (only) what they say they do. The only thing a duration of instantaneous means is that the spell is too short to dispel. It does not mean the spell cannot have different but sequential effects within the same, undefined, 'instant'. This may be counterintuitive to a natural English sense of the word 'instantaneous', but in this case the word is a defined game term, so we use its defined meaning, not the English meaning.}

_{As proof of that, we have other instantaneous spells that call for sequential effects. Consider the Lightning Lure spell, which has a duration of instantaneous (emphases mine):}

_{You create a lash of lightning energy that strikes at one creature of your choice that you can see within 15 feet of you. The target must succeed on a Strength saving throw or be pulled up to 10 feet in a straight line toward you and then take 1d8 lightning damage if it is within 5 feet of you.}

_{In this case there is a far range effect that provokes a save, if that save is failed the target is moved, if the target is moved sufficiently it ends up in the range of a new effect and then it takes damage. The movement and damage take effect at separate, discrete points in time despite the fact that the overall spell is 'instantaneous'; the damage comes after the movement and only if the result of the movement brings the target sufficiently close. We know that the movement and damage take place at different instants of time because of the phrase "and then". The spell can do this because instantaneous does not mean the duration of the spell is no time, it means that the duration is less than the time required to cast dispel magic.}

Answer 2

Yes, it deals damage to the original target first

Chain Lightning says:

You create a bolt of lightning that arcs toward a target of your choice that you can see within range. Three bolts then leap from that target to as many as three other targets,

The implication is that it hits the first target before the other targets.

Answer 3

DM's call

This is clearly something the DM should adjudicate. The wording is sufficiently complex, and D&D shouldn't be about tiny rule corner cases.

Xanathars Guide to Everything (p. 77)

An optional rule is that:

If two or more things happen at the same time on a character or monster's turn, the person at the game table - whether player or DM - who controls that creature decides the order in which those things happen.

Arguably the lightning damage and concentration saving throws are all happening at the same time. So under this rule, the controller of the active creature -- probably the DM -- decides.

Making the Bless caster save first and then do a concentration check is beneficial to the active creature. Then do the same for the Haste concentrating creature. Then finally on the Hasted creatures, so it is possibly denied its advantage on dex saves.

Read the Spell itself

You create a bolt of lightning that arcs toward a target of your choice that you can see within range. Three bolts then leap from that target to as many as three other targets, each of which must be within 30 feet of the first target.

This part describes targeting. The bolt goes after one target, then shoots out to other targets.

[SNIP] restrictions on targets.

A target must make a Dexterity saving throw. The target takes 10d8 lightning damage on a failed save, or half as much damage on a successful one.

The spell then describes damage.

There is more than one reasonable way to read this.

1. You inject these into the previous targetting sequence. So you target the first creature, then you make it roll a dex save and deal damage. Then you pick 3 other targets and for each one you pick you do the same.

2. You do it in two waves. One for the first target, and then one for the other targets.

3. You evaluate damage after all of the targets are picked. The damage occurs in one wave.

All 3 are perfectly reasonable readings of the spell.

The targeting is clearly A then B, but the effect is not clearly required to occur at the same sequence as the targeting.

To make this clear, imagine a spell that read much like chain lighting, but ended differently:

You create a beam of energy that shoots toward a target of your choice that you can see within range. Three beams then leap from that target to as many as three other targets, each of which must be within 30 feet of the first target. Add up all of the targeted creature's HP, and take the average. All creatures are set to this amount of HP (limited by their max HP).

This spell makes perfect sense. There is no real conflict between the first half and second half. Yet the second half only makes sense if it happens all at once.

To me, this demonstrates that the then in the first part could imply a sequence to the effect, but does not demand it.

Which in turn means that either reading is reasonable; a claim that one reading or the other is the only correct one is wrong.

What I'd do as DM

Making saving for an area of effect spell be sequenced is annoying. So I'd just have everyone save and do concentration checks in parallel. Effects of the failed saves and the like would be evaluated after this parallel process.

As the DM, I'm in charge of the game's difficulty dials anyhow; I'd rather the mechanics be faster than the fight be harder, because I can make fights harder by fiat anyhow.